Scanning probe microscopy is one of the most versatile windows into the nanoworld, providing imaging access to a variety of electronic(1), dielectric(2), magnetic(3) and topographic(4,5) sample properties, depending on the probe used. Here, we demonstrate a scanning probe imaging method that extends the range of accessible quantities to label-free imaging of chemical species while operating on arbitrary samples-including insulating materials-under ambient conditions. Moreover, its sensitivity extends below the surface of a sample, allowing for imaging of subsurface features. We achieve these results by recording NMR signals from a sample surface with a recently introduced scanning probe, a single nitrogen-vacancy centre in diamond. We demonstrate NMR imaging with 10 nm resolution and achieve chemically specific contrast by separating fluorine from hydrogen-rich regions. Our result opens the door to scanning probe imaging of the chemical composition and molecular structure of arbitrary samples. A method with these abilities will find widespread application in materials science, even on biological specimens down to the level of single macromolecules.